punkieys17
- Feb 7, 2016
- 45
- Joined
- Feb 7, 2016
- Messages
- 45
So this is the simplest Mosfet circuit possible. Its in a shower pump I bought as a backup. The mains input (230vAC) comes to one side of the mosfet (BTA08 600b). A feed to the gate goes via a resistor (12k) and two reed switches which are triggered closed by magnetic floats in the pump. The pump died when the starting capacitor went. On replacing it the pump would come on on its own. I have replaced the mosfet (twice!) and the resistor. The pump has two reed switches mounted outside each end of the twin impellers pumps - one for hot water and one for cold. The switches are mounted in parallel so turning on either hot or cold will cause the magnetic float to rise and trigger the reed switch. One reed switch is connected with the black wires - and with just that connected the pump doesnt trigger till the float rises. However connecting the white wires, which are connected to the same PCB lands, causes the motor to trigger. The motor is not fully on its as if an intermittent connection is being made. However the circuit measures open circuit. The wires were originally the same (black) but changed them to the white to eliminate that as a potential error source. I have swapped where the white and black wires are soldered onto the PCB to ensure its not a simple PCB problem. There is plenty of space between the PCB lands and no question of something shorting - it measures open circuit. The circuit (BTA08 600B and 12k resistor) is exactly the same as the same commercial pump installed and working (Techflow 45). To ensure it wasn't picking up an ac circuit I wrapped the white wires temporarily in silver foil as shielding - with no change.
So I have 2 reed switches as triggers, both show no continuity until triggered by the magnets yet when I connect the white wires the motor stutters into life. If I put a magnetic field close to the reed switch while the motor is stuttering it fires into full life. Connecting just the black wire reed switches it works correctly. Connecting only the white the motor is triggered. I have even had the reed switch suspended in air to ensure no magnetic field -yet motor starts but no connection shows on a meter.
Any thoughts please. I have replaced the wires, switched the wires, replaced the reed switches, the mostfet and the resistor ..............I'm at a complete loss
So I have 2 reed switches as triggers, both show no continuity until triggered by the magnets yet when I connect the white wires the motor stutters into life. If I put a magnetic field close to the reed switch while the motor is stuttering it fires into full life. Connecting just the black wire reed switches it works correctly. Connecting only the white the motor is triggered. I have even had the reed switch suspended in air to ensure no magnetic field -yet motor starts but no connection shows on a meter.
Any thoughts please. I have replaced the wires, switched the wires, replaced the reed switches, the mostfet and the resistor ..............I'm at a complete loss